core research on solid oxide fuel cells, plus flexible ... · the design of improved current...
TRANSCRIPT
Professor Nigel Brandon OBE FREng
BG Chair in Sustainable Gas
Imperial College London
Director: Hydrogen and Fuel Cell SUPERGEN Hub (H2FC SUPERGEN)
www.h2fcsupergen.com
Core Research on Solid Oxide Fuel Cells, plus flexible
funding project “Application of 3D imaging and analysis to
the design of improved current collectors for SOFCs.”
www.imperial.ac.uk/energyfutureslab
Content
• Core - 3D Imaging and Analysis of Solid Oxide Fuel Cell
Electrodes.
• Flexible - Application of 3D imaging and analysis to the design
of improved current collectors for SOFCs
• Core - New approaches to SOFC electrode fabrication.
• Summary.
Ambition – to move to a move towards a design led approach to
optimum SOFC electrodes
Typical planar SOFC geometries
Brett DJL, Atkinson A, Brandon NP, Skinner SJ, Intermediate temperature solid oxide fuel cells, CHEM SOC REV, 2008, Vol:37,
Pages:1568-1578
SOFC Electrode Design
Illustration of the effect of extending the TPB using a MIEC electrolyte. (a)
Electrolyte / cermet anode with active TPB circled; (b) mechanism of
reaction at the TPB; (c) mechanism of reaction at the extended TPB.
Page 6
Tomography techniques to resolve 3D microstructure
0.1 nm 10 nm 1µm 100µm
10
nm
3
1µ
m3
1
00
µm
3
1
0m
m3
3D Atom
Probe
Voxel Length Scale
Vo
lum
e S
ize A
naly
sis
Electron
Tomo
Dual Beam
FIB Tomo
X-ray NCT
X-ray
Microtomogaphy
CT/Synchrotron
Mechanical
Sectioning
Combine multiple
tomographic techniques
Functional Materials
Multi-scale Tomography
FOV/Resolution
We can apply this to
SOFC/LIB electrodes
And other materials
………
1cm >1m
>1
m3
1mm 1mm
Farid Tariq et al, Acta Materialia 59(5),2011 Diagram After Uchic and Holzer, MRS Bulletin, 2007
Tomography of Ni-ScSZ electrodes
• Allows feature extraction (Ni/ScSZ/Pores)
• FIBSEM, voxel sizes ~20-50nm
• 1350ºC sintering, 1 hr at temperature,
reduced
A
5 µm 5 µm 5 µm
Ni
30 Vol.%
Ni
40 Vol.%
Ni
50 Vol.%
Ni Ni
ScSZ ScSZ
Pores Pores
Pores
B C
Ni Percolation Threshold
Ni Percolated
Fabrication and characterization of Ni/ScSZ cermet anodes for IT-SOFCs, Somalu MR, Yufit V, Cumming D, Lorente E, Brandon NP,
INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 2011, Vol:36, Pages:5557-5566.
Percolated nickel networks
• Ni30 – 65% of Ni is
percolated
A
5 µm 5 µm 5 µm
Ni
30 Vol.%
Ni
40 Vol.%
Ni
50 Vol.%
Ni Ni B C
Considered Ni
Percolation Threshold Considered Ni Percolated Considered Ni Percolated
• Ni40 – 97% of Ni is
percolated
• Ni50 – 90% of nickel is
percolated
Preliminary results indicate:
Ni 646
Pores 1317
ScSZ 1345
Ni 2481
Pores 2976
ScSZ 4195
Ni 1594
Pores 1999
ScSZ 2130
Surface Area of particles in total volume analysed (x 103 m-1)
Advanced Analysis: 3D Interface Changes Ni30-Ni50
Page 2
A
8 µm
Ni
30 Vol.%
Ni
ScSZPores
Ni Percolation Threshold
Ni
50 Vol.%
Ni
Ni Percolated
B
• Auriga Zeiss, 5kV, SEI, 1nA
• 100-200 Images
• Feature extraction (Ni/ScSZ/Pores)
• FIBSEM, voxel sizes ~20-30nm
• 1350ºC sintering, 2 hr at temperature
• Ni 30% has some particles forming percolated
networks and other particles separate
• Ni content >30% is very well connected
M.Samalu et al, Intl Journal of Hydrogen Energy 36(9),2011
Advanced Analysis of 3D Microstructure Changes
Page 4
10 µm
A B C
D E
5 µm
Example: Particles of NickelNecks between adjacent particles :
Percolation, sintering and strain
3D imaging and quantification of interfaces in SOFC anodes, F. Tariq, M.Kishimoto, V.Yufit, G.Cui, M.Somalu and N.Brandon (Journal of European Ceramic Society, In Press & Available May 2014)
3D Interfaces: Structure-property-behaviour
Page 15
Experimental, Analytical and Modeling Results
0
2
4
6
Expt Sim Ratio
0
1
2
Expt Sim Ratio
0
1
2
Expt Sim Ratio
Ni-Ni ScSZ-ScSZ Ni-ScSZ
N/A
Ni30ScSZ Ni50ScSZ Ratio Conductivity
Change
Young's
Modulus
TPB
Density
Ni-Ni necks
(nm2/nm3)
2.7x10-4 3.55x10-4 1.32
Resistance:3.5
Expt. – 4
Sim. – 3.7
ScSZ-ScSZ necks
(nm2/nm3)
4.86x10-4 3.22x10-4 1.5 Expt. -
1.4±0.1
Sim. - 1.1
Ni-ScSZ necks
(nm2/nm3)
15.7x10-4 19.5x10-4 1.2 Expt. - 1.1
Sim. – N/A
Neck Experimentally Measured and Modelled
3D imaging and quantification of interfaces in SOFC anodes, F. Tariq, M.Kishimoto, V.Yufit, G.Cui, M.Somalu and N.Brandon (Journal of European Ceramic Society, In Press & Available May 2014)
For electrical conductivity any contact (e.g. more necks) would cause a larger expt. conductivity increase
Most (though not all) load is passed through ceramic matrix
SOFC Tomography and Modelling
Unanswered Questions
Definition of Ni-YSZ Interface?
Self-Contact?
Fatigue/Cracking Behaviour?
Mechanisms at work
Schematic from P.J.Withers, Adv. Eng.
Materials, 2011
LSCF Electrode Imaging and Modelling
2 µm
Porosity
LSCF
Phases
Advanced 3D Imaging and Analysis of SOFC Electrodes F.Tariq, M.Kishimoto, S.J Cooper, P.Shearing , N.P.Brandon, ECS Trans, 2013 Microstructural Analysis of an LSCF Cathode using in-situ tomography and simulation S.J Cooper, M.Kishimoto, F.Tariq, R.Bradley, A.Marquis, N.P.Brandon, J.Kilner, P.Shearing , ECS Trans, 2013
700°C
Flow Modelling in Porous structures
- Pressure gradient calculated across
microstructure
- This can be used to calculate permeability
- A measure of how much fluid could pass
through this type of structure
(Pa)
Higher pressure
5 µm
Low pressure
Fluid Inlet
Application of 3D imaging and analysis to the design of improved current collectors for SOFCs
N Brandon, A Atkinson & Z Chen with Ceres Power
© Ceres Power 2013 Title: 8th International Smart Hydrogen and Fuel Cell Conference Rev: 1.0
• Thin steel substrate with even
thinner layers of active SOFC
materials coated on top
• Low temperature electrolyte (ceria)
enables operation at <600 oC
• Key advantages:
– Low cost cells
– Compact, lightweight design
– Mechanically tough
– Simple & reliable stack sealing
– Enables low cost balance of plant
The core of the Ceres proposition is its unique metal-supported cell
10
Stainless Steel Substrate
Anode Layer
Ceria ElectrolyteLayer
Cathode Layer
FUEL
AIR
ELECTRICITY
Indentation FEM
Simulation
Indentation
experiment on
bulk/films/cells
Response curves
Experiment
Elastic
properties
Response curves
3D models by
FIB/SEM
tomography
3D models with
different material
constitutives
Elastic properties
Compression FEM
Fracture criteria prediction with
varied current collector designs
Electrode structure
optimisation
Electrolyte failure
estimation
Methodology
Compare and validate the models
As FEM input parameters
Axisymmetric modelling of mechanical
indentation into electrodes
Indentation process in axisymmetric modelling (a) before
indentation, (b) loading to a maximum depth, and (c)
complete unloading generated residual depth.
Nano-indentation curves for porous LSCF
cathodes
0
100
200
300
400
500
0 800 1600 2400 3200 4000
Lo
ad
(m
N)
Indentation depth (nm)
900°C_Experiment
0
50
100
150
200
250
300
0 400 800 1200 1600 2000
Load
(m
N)
Indentation depth (nm)
1000°C_Experiment
1000°C_Simulation
0
50
100
150
200
250
300
0 200 400 600 800 1000
Lo
ad
(m
N)
Indentation depth (nm)
1100°C_Experiment
0
10
20
30
40
50
60
70
80
0 40 80 120 160
Load
(m
N)
Indentation depth (nm)
1200°C_Experiment
1200°C_Simulation
Comparison of load vs. depth curves for models with varying porosities resulted from different
sintering temperatures. Porous LSCF sintered at different temps, 50 to 30 vol% porous, pellet,
spherical indenter, 25 mm radius, RT data
Results: elastic modulus and hardness
Sintering
temperature
(°C)
Method hmax (nm) Pmax (mN) S (mN/nm) a (nm) E (GPa) H (GPa)
900 Experiment
4008.4 437.9 1.05 13079.4 34.1 0.83
Simulation 409.5 1.13 13146.3 36.1 0.75
1000 Experiment
1973.4 241.4 0.89 9221.2 47.2 0.90
Simulation 246.4 0.93 9256.5 47.2 0.91
1100 Experiment
950.1 252.2 1.02 6136.2 75.9 2.19
Simulation 258.2 1.04 6137.0 71.6 2.18
1200 Experiment
164.1 67.5 0.86 2294.7 189.3 4.03
Simulation 68.2 0.78 2241.1 173.9 4.17
Comparison of elastic modulus and hardness results determined by experiment and simulation
Electrode fabrication: porous scaffold
YSZ
Pore former
Slurry Co-sintering
T > 1300 C
YSZ
Tape casting or
screen printing
CGO
Mixture of commercial powder and nano-powder
(supplied by Prof Jawwad Darr, UCL)
Porous CGO
State of the art electrodes: Impregnation of porous scaffolds
550ºC, 1 h
+
heating & cooling
n times
Metal nitrate solution Porous
scaffold
Infiltration
Decomposition
To oxide
University of St Andrews
University of Pennsylvania
FIB-SEM: 1 x infiltration
Before reduction After reduction
CGO NiO Ni
Enhanced triple phase boundary density in infiltrated electrodes for SOFCs, M Kishimoto, M Lomberg, E Ruiz-Trejo and N P Brandon, J Power
Sources, 2014, Vol:266, Pages:291-295..
3D reconstruction Ni x 1 -GDC
GDC Ni Ni-GDC
TPB (with GDC) Ni (with GDC) TPB
4.2 μm
Enhanced triple phase boundary density in infiltrated electrodes for SOFCs, M Kishimoto, M Lomberg, E Ruiz-Trejo and N P Brandon, J Power
Sources, 2014, Vol:266, Pages:291-295..
3D reconstruction Ni(10)-GDC
GDC Ni Ni-GDC
TPB (with GDC) Ni (with GDC) TPB
7.5 μm
Enhanced triple phase boundary density in infiltrated electrodes for SOFCs, M Kishimoto, M Lomberg, E Ruiz-Trejo and N P Brandon, J Power
Sources, 2014, Vol:266, Pages:291-295..
Quantification
GDC scaffold Ni(1)-GDC Ni(10)-GDC Conventional
Ni-YSZ
Volume fraction
[%]
Ni 0.00 1.29 19.8 25.3
GDC 57.1 56.9 60.2 25.1
Pore 42.9 41.8 20.1 49.6
Particle/pore size
[μm]
Ni N/A 0.102 0.354 1.38
GDC 0.844 0.748 0.706 0.730
Pore 0.667 0.594 0.300 1.74
TPB density
[μm/μm3]
N/A 11.0 18.4 2.49
Enhanced triple phase boundary density in infiltrated electrodes for SOFCs, M Kishimoto, M Lomberg, E Ruiz-Trejo and N P Brandon, J Power
Sources, 2014, Vol:266, Pages:291-295..
Electrolyte Supported Cell Fabrication and Testing
26
16mm
1mm
11mm
20mm
270μm 10-20μm
10-20μm
(Air) (Fuel)
Counter Electrode (CE)
Reference Electrode (RE)
Working Electrode (WE)
Electrolyte
Screen Printed commercial LSCF-GDC Commercial electrolyte, YSZ Screen Printed GDC, sintered at 1350˚C
2M Ni(NO3)2
Ni(NO3)2 decomposition at 500˚C
• 20-80% H2
• 550-750˚C
M Lomberg, E Ruiz-Trejo, G Offer and N P Brandon, Characterization of Ni-Infiltrated GDC Electrodes for Solid
Oxide Cell Applications, J Electrochem. Soc., 2014, accepted for publication
Impedance Spectroscopy Results
27
0.00 0.05 0.10 0.15 0.200.00
0.05
0.10
0.15
L1 R_hfi R_h
CPE1
R_l
CPE2
Element Freedom Value Error Error %
L1 Free(+) 1.9281E-07 N/A N/A
R_hfi Free(+) 1.271 N/A N/A
R_h Free(+) 0.24069 N/A N/A
CPE1-T Free(+) 1.818 N/A N/A
CPE1-P Free(+) 0.54251 N/A N/A
R_l Free(+) 0.092636 N/A N/A
CPE2-T Free(+) 0.017949 N/A N/A
CPE2-P Free(+) 0.59862 N/A N/A
Data File:
Circuit Model File: C:\Users\ml2610\Dropbox\PhD\Sync folders
from IC desk\3 On going\Experimental Da
ta\Experimental 10xNi-CGO-YSZ-LSCF-CGO\2
4-01-2013\All data files\FRA data\high t
emperature_2.mdl
Mode: Run Fitting / Selected Points (0 - 0)
Maximum Iterations: 100
Optimization Iterations: 0
Type of Fitting: Complex
Type of Weighting: Calc-Modulus
0.6kHz
3.4kHz
580oC
690oC
750oC
Fitting
-Z''
(cm
2)
Z' (cm2)
2.5kHz
10 times Ni-infiltrated GDC electrode, P(H2)=0.5atm, 100k-0.1Hz, OCV
M Lomberg, E Ruiz-Trejo, G Offer and N P Brandon, Characterization of Ni-Infiltrated GDC Electrodes for Solid
Oxide Cell Applications, J Electrochem. Soc., 2014, accepted for publication
Summary
•Progress continues to be made in the application and interpretation
of 3D imaging to understand SOFC electrodes structures, and how
these relate to performance.
•In the next 12 months we will be able to leverage new EPSRC
capital investments in imaging and characterisation tools and additive
manufacturing.
• Our ultimate ambition is to move towards a design led approach to
SOFC fabrication, and to develop in-silico accelerated ageing
methodologies, in order to optimise both performance and lifetime of
operating devices.
Acknowledgements
•3D imaging and analysis–Dr. Farid Tariq, Dr. Masashi Kishimoto, Dr
Khalil Rhazoui, Prof Claire Adjiman, Dr Qiong Cai (Surrey), Guansen
Cui, Sam Cooper, Dr. Paul Shearing (UCL), Prof. Peter Lee and Dr.
Dave Eastwood (Manchester).
•Scaffold electrodes– Dr Enrique Ruiz-Trejo, Dr Paul Boldrin, Marina
Lomberg, Zadariana Jamil, Prof Jawwad Darr (UCL).
•The EPSRC for funding.
•Current collector Project collaborators Ceres Power.